This is needed to access widgets to make the shell adaptive.
This also adds libhandy as a submodule and will make use of that version
if it isn't available otherwise.
Meson is a build system focused on speed an ease of use, which
helps speeding up the software development. This patch adds meson
support along autotools.
https://bugzilla.gnome.org/show_bug.cgi?id=785414
In order to share the libgd and gvc modules between autotools and
meson, this patch moves their directories to subprojects
directory and updates autotools.
https://bugzilla.gnome.org/show_bug.cgi?id=785414